Allelic variation in sugary1 gene affecting kernel sweetness among diverse-mutant and -wild-type maize inbreds

Sweet corn is popular worldwide as vegetable. Though large numbers of sugary1 (su1)-based sweet corn germplasm are available, allelic diversity in su1 gene encoding SU1 isoamylase among diverse maize inbreds has not been analyzed. Here, we characterized the su1 gene in maize and compared with allied species. The entire su1 gene (11,720 bp) was sequenced among six mutant (su1) and five wild (Su1) maize inbreds. Fifteen InDels of 2-45 bp were selected to develop markers for studying allelic diversity in su1 gene among 19 mutant- (su1) and 29 wild-type (Su1) inbreds. PIC ranged from 0.15 (SU-InDel7) to 0.37 (SU-InDel13). Major allele frequency varied from 0.52 to 0.90, while gene diversity ranged from 0.16 to 0.49. Phylogenetic tree categorized 48 maize inbreds in two clusters each for wild- type (Su1) and mutant (su1) types. 44 haplotypes of su1 were observed, with three haplotypes (Hap6, Hap22 and Hap29) sharing more than one genotype. Further, comparisons were made with 23 orthologues of su1 from 16 grasses and Arabidopsis. Maize possessed 15-19 exons in su1, while it was 11-24 exons among orthologues. Introns among the orthologues were longer (77-2206 bp) than maize (859-1718 bp). SU1 protein of maize and orthologues had conserved α-amylase and CBM_48 domains. The study also provided physicochemical properties and secondary structure of SU1 protein in maize and its orthologues. Phylogenetic analysis showed closer relationship of maize SU1 protein with P. hallii, S. bicolor and E. tef than Triticum sp. and Oryza sp. The study showed that presence of high allelic diversity in su1 gene which can be utilized in the sweet corn breeding program. This is the first report of comprehensive characterization of su1 gene and its allelic forms in diverse maize and related orthologues.